The proposed research will study normal and pathological human auditory nerve action potentials (APs) and cochlear potentials recorded from external ear canal and brainstem evoked responses (ABRs) recorded from vertex. The project includes investigations relevant to the problems of using these responses to quantify auditory system pathology (by predicting the puretone audiogram) and to localize it. Cochlear excitation patterns generated by frequency specific clicks will be investigated with the derived AP technique, by recording single unit activity from animals, and by computer modeling. The relationship between frequency specific click AP and ABR waveforms to the underlying cochlear excitation patterns in normal and pathological ears will then be determined. The project also includes research designed to further investigate previous results which suggest that pathologically enlarged summating potential relates specifically to the histopathologic condition known as endolymphatic hydrops. Data will be collected from a larger series of patients to confirm the validity of a previously demonstrated relationship between summating potential enlargement and Meniere's disease, and also to investigate effects of duration of pathology and severity of hearing loss on the summating potential.